This disclosure is directed to a method of determining leakage flow rate from a perforation or tear in a geomembrane. A geomembrane is defined as a sheet typically made of pliable plastic material. It is normally used to form a shallow pond in an embankment or other impoundment to store liquids. On the one hand, it may be a pond for storing potable water. On the other hand, it can be used to store toxic waste, or the like. In general terms, the impoundment is a shallow pond with a surrounding wall or bank. The pond is lined with the geomembrane, typically applied in single or multiple layers. The geomembrane is formed of several sheets which are joined at seams thereby defining the impoundment. The plastic sheet material thus forms an impermeable membrane. When a leak occurs, this can be disastrous to groundwater supplies, aquifers, and can otherwise create hazards for those who use such water supplies. The rate of leakage may vary widely. For instance, if the impermeable geomembrane is placed over a relatively impervious layer of clay, the leakage rate may be substantially zero. On the other hand, the soil beneath the geomembrane may be highly permeable and the leakage rate can be quite high. It is important to know the rate of leakage once a leak has been located. This is important so that the nature and extent of repair activity for the leak can then be determined. For instance, if there is a tear, but the leakage rate is negligible, the need for implementing repairs is not critical. However, if the leak rate is quite high, it is necessary to make a quick repair. Electrical leak detection methods alone cannot determine the amount of liquid leakage through a leak. If, over a long period of time, the liquid that has leaked through the hole has saturated the soil in a large area under the leak, or if the underside of the membrane is in contact with the ater table, or phreatic zone, the electrical measurement will only be affected by the accumulated liquids (electrolytes) not by the liquid leakage rate. The method in this disclosure, which incorporates an electrical detecton device in the apparatus will indicate the leakage rate.